Added a simple example (could use more, but at least it has one now)

git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@152214 c90b9560-bf6c-de11-be94-00142212c4b1

reference/exec/functions/exec.xml

@@ -1,5 +1,5 @@
 <?xml version="1.0" encoding="iso-8859-1"?>
-<!-- $Revision: 1.10 $ -->
+<!-- $Revision: 1.11 $ -->
 <!-- splitted from ./en/functions/exec.xml, last change in rev 1.2 -->
   <refentry id="function.exec">
    <refnamediv>
@@ -39,6 +39,20 @@
      return status of the executed command will be written to this
      variable.
     </para>
+    <para>
+     <example>
+      <title>An <function>exec</function> example</title>
+      <programlisting role="php">
+<![CDATA[
+<?php
+// outputs the username that owns the running php/httpd process
+// (on a system with the "whoami" executable in the path)
+echo exec('whoami');
+?>
+]]>
+      </programlisting>
+     </example>
+    </para>
     &warn.escapeshell;
     &note.exec-bg;
     &note.exec-path;